1. Field of the Invention
The present invention is directed to an acceleration sensor, and in particular to an acceleration sensor constructed on an SOI (silicon-on-insulator) substrate, for exact measurement of minute accelerations, as well as to a method for manufacturing such an acceleration sensor.
2. Description of the Prior Art
Modern navigation systems as well as safety systems in the automotive field require reliable acceleration sensors which are small and simple to manufacture, and which have a high measuring precision and a good proportionality between the measured quantity and the corresponding output signal. Conventionally manufactured acceleration sensors, by contrast, are relatively large, expensive and imprecise. In response to these deficiencies, various forms of micromechanical acceleration sensors have been devised as described, for example, in the article "Silicon Micromechanics: Sensors and Actuators on a Chip," Howe et al., IEEE Spectrum, July 1990, pages 29-35. In such known micromechanical acceleration sensors, however, polysilicon layers are used for the manufacture of the mechanically moving parts. As a consequence, the mechanical long-term stability of these parts is inadequate under certain circumstances in comparison to the expected service life of the systems in which they are utilized. In addition to the possible degradation over time, the mechanical properties of such parts, such as the modulus of elasticity and the intrinsic stress of the layers, are sensitively dependent on the particular manufacturing conditions. The thermal curing of the intrinsic stress of the layers, for example, requires additional temperature steps in the manufacturing process, which have a disadvantageous effect on the simultaneously manufactured electronics which are integrated in the sensor. Moreover, long-lasting and complicated depositions of semiconductor layers are necessary.